This invention relates to novel potassium channels and genes encoding these channels. More specifically the invention provides isolated polynucleotides encoding the KCNQ5 potassium channel subunit, cells transformed with these polynucleotides, transgenic animals comprising genetic mutations, and the use of the transformed cells and the transgenic animals for the in vitro and in vivo screening of chemical compounds affecting KCNQ5 subunit containing potassium channels.
Potassium channels participate in the regulation of electrical signalling in excitable cells, and regulates the ionic composition of biological fluids. Mutations in the four known genes of the KCNQ branch of the K+-channel gene family underlie inherited cardiac arrhythmia""s, in some cases associated with deafness, neonatal epilepsy, and the progressive hearing loss of the elderly (presbyacusis).
Ion channels play important roles in signal transduction and in the regulation of the ionic composition of intra- and extracellular fluids. KCNQ1 is a typical member of the voltage-gated potassium channel superfamily with 6 transmembrane domains and a pore region situated between the fifth and the sixth transmembrane domain. The minK protein (also known as KCNE1 or lsK) has a single transmembrane span and cannot form potassium channels on its own. However, as a xcex2-subunit it enhances and modifies currents mediated by KCNQ1. These heteromeric channels participate in the repolarization of the heart action potential. Certain mutations in either KCNQ1 or KCNE1 cause a form of the autosomal dominant long QT syndrome (LQTS), a disease characterised by repolarization anomalies of cardiac action potentials resulting in arrhythmias and sudden death. Interestingly, other mutations in either gene lead to the recessive Jervell and Lange-Nielsen (JLN) syndrome that combines LQTS with congenital deafness. In order to cause deafness, KCNQ1/minK currents must be reduced below levels that are already sufficiently low to cause cardiac arrhythmia.
Mutated and non-mutated KCNQ2 and KCNQ3 potassium channels have been disclosed in WO 99/07832, WO 99/21875 and WO 99/31232.
We have now cloned and characterised KCNQ5, a novel member of the KCNQ family of potassium channel proteins. KCNQ5 forms heteromeric channels with other KCNQ channel subunits, in particular KCNQ3 and KCNQ4.
The present invention has important implications for the characterisation and exploitation of this interesting branch of the potassium channel super family.
Accordingly, in its first aspect, the invention provides an isolated polynucleotide having a nucleic acid sequence which is capable of hybridising under at least medium stringency conditions with the polynucleotide sequence presented as SEQ ID NO: 1, its complementary strand, or a sub-sequence thereof.
In another aspect the invention provides a recombinantly produced polypeptide encoded by the polynucleotide of the invention.
In a third aspect the invention provides a cell genetically manipulated by the incorporation of a heterologous polynucleotide of the invention.
In a fourth aspect the invention provides a method of screening a chemical compound for inhibiting or activating or otherwise modulating the activity on a potassium channel comprising at least one KCNQ5 channel subunit, which method comprises the steps of subjecting a KCNQ5 channel subunit containing cell to the action of the chemical compound; and monitoring the membrane potential, the current, the potassium flux, or the secondary calcium influx of the KCNQ5 channel subunit containing cell.
In a fifth aspect the invention relates to the use of a polynucleotide sequence of the invention for the screening of genetic materials from humans suffering from neurological diseases for mutations in the KCNQ5 gene.
In a sixth aspect the invention relates to the chemical compound identified by the method of the invention, in particular to the use of such compounds for diagnosis, treatment or alleviation of a disease related to diseases or adverse conditions of the CNS, including affective disorders, Alzheimer""s disease, anxiety, ataxia, CNS damage caused by trauma, stroke or neurodegenerative illness, cognitive deficits, compulsive behaviour, dementia, depression, Huntington""s disease, mania, memory impairment, memory disorders, memory dysfunction, motion disorders, motor disorders, neurodegenerative diseases, Parkinson""s disease and Parkinson-like motor disorders, phobias, Pick""s disease, psychosis, schizophrenia, spinal cord damage, stroke, tremor, seizures, convulsions and epilepsy.
In a seventh aspect the invention provides a transgenic animal comprising a knock-out mutation of the endogenous KCNQ5 gene, a replacement by or an additional expression of a mutated KCNQ5 gene, or genetically manipulated in order to over-express the KCNQ5 gene or to over-express mutated KCNQ5 gene.
In an eighth aspect the invention relates to the use of the transgenic animal of the invention for the in vivo screening of therapeutic compounds.
Other objects of the invention will be apparent to the person skilled in the art from the following detailed description and examples.
The present invention provides novel potassium channels and genes encoding these channels. The invention also provides cells transformed with these genes, transgenic animals comprising genetic mutations, and the use of the transformed cells and the transgenic animals for the in vitro and in vivo screening of drugs affecting KCNQ5 containing potassium channels.
In its first aspect, the invention relates to novel nuceic acid molecules encoding a polypeptide comprising all or a portion of a KCNQ5 protein.
In a preferred embodiment, the polynucleotides of the invention are such which have a nucleic acid sequence capable of hybridising under at least medium stringency conditions with the polynucleotide sequence presented as SEQ ID NO: 1, its complementary strand, or a sub-sequence thereof.
The polynucleotides of the invention include DNA, cDNA and RNA sequences, as well as anti-sense sequences, and include naturally occurring, synthetic, and intentionally manipulated polynucleotides. The polynucleotides of the invention also include sequences that are degenerate as a result of the genetic code.
As defined herein, the term xe2x80x9cpolynucleotidexe2x80x9d refers to a polymeric form of nucleotides of at least 10 bases in length, preferably at least 15 bases in length. By xe2x80x9cisolated polynucleotidexe2x80x9d is meant a polynucleotide that is not immediately contiguous with both of the coding sequences with which it is immediately contiguous (one on the 5xe2x80x2 end and one on the 3xe2x80x2 end) in the naturally occurring genome of the organism from which it is derived. The term therefore includes recombinant DNA which is incorporated into an expression vector, into an autonomously replicating plasmid or virus, or into the genomic DNA of a prokaryote or eukaryote, or which exists as a separate molecule, e.g. a cDNA, independent from other sequences.
The polynucleotides of the invention also include allelic variants and xe2x80x9cmutated polynucleotidesxe2x80x9d having a nucleotide sequence that differs from the sequence presented as SEQ ID NO: 1 at one or more nucleotide positions. The mutated polynucleotide may in particular be a polynucleotide of the invention having a nucleotide sequence as in SEQ ID NO: 1, which sequence, however, differs from SEQ ID NO: 1 so as to effect the expression of a variant polypeptide. The mutated polynucleotide may be a polynucleotide of the invention having a nucleotide sequence encoding a potassium channel having an amino acid sequence that has been changed at one or more positions. The mutated polynucleotide may in particular be a polynucleotide of the invention having a nucleotide sequence encoding a potassium channel having an amino acid sequence that has been changed at one or more positions located in the conserved regions, as defined by Table 1, below.
Hybridisation Protocol
The polynucleotides of the invention are such which have a nucleic acid sequence capable of hybridising with the polynucleotide sequence presented as SEQ ID NO: 1, its complementary strand, or a sub-sequence thereof, under at least medium, medium/high, or high stringency conditions, as described in more detail below.
In a preferred embodiment the polynucleotide is a fragment of at least 15 bases in length which is sufficient to permit the fragment to hybridise to DNA that encodes a polypeptide of the invention, preferably the polypeptide having the amino acid sequence presented as SEQ ID NO: 2 under at least medium, medium/high, or high stringency conditions, as described in more detail below.
Suitable experimental conditions for determining hybridisation between a nucleotide probe and a homologous DNA or RNA sequence, involves pre-soaking of the filter containing the DNA fragments or RNA to hybridise in 5xc3x97SSC [Sodium chloride/Sodium citrate; cf. Sambrook et al.; Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Lab., Cold Spring Harbor, N.Y. 1989] for 10 minutes, and pre-hybridisation of the filter in a solution of 5xc3x97SSC, 5xc3x97Denhardt""s solution [cf. Sambrook et al.; Op cit.], 0.5% SDS and 100 xcexcg/ml of denatured sonicated salmon sperm DNA [cf. Sambrook et al.; Op cit.], followed by hybridisation in the same solution containing a concentration of 10 ng/ml of a random-primed [Feinberg A P and Vogelstein B; Anal. Biochem. 1983 132 6-13], 32P-dCTP-labeled (specific activity  greater than 1xc3x97109 cpm/xcexcg) probe for 12 hours at approximately 45xc2x0 C.
The filter is then washed twice for 30 minutes in 2xc3x97SSC, 0.5% SDS at a temperature of at least at least 60xc2x0 C. (medium stringency conditions), preferably of at least 65xc2x0 C. (medium/high stringency conditions), more preferred of at least 70xc2x0 C. (high stringency conditions), and even more preferred of at least 75xc2x0 C. (very high stringency conditions).
Molecules to which the oligonucleotide probe hybridises under these conditions may be detected using a x-ray film.
DNA Sequence Homology
In a preferred embodiment, the polynucleotides of the invention show a homology of at least 65%, preferably at least 70%, more preferred at least 80%, even more preferred at least 90%, most preferred at least 95%, with the polynucleotide sequence presented as SEQ ID NO: 1.
As defined herein, the DNA sequence homology may be determined as the degree of identity between two DNA sequences indicating a derivation of the first sequence from the second. The homology may suitably be determined by means of computer programs known in the art such as GAP provided in the GCG program package [Needleman S B and Wunsch C D, Journal of Molecular Biology 1970 48 443-453] using default parameters suggested herein.
Cloned Polynucleotides
The isolated polynucleotide of the invention may in particular be a cloned polynucleotide.
As defined herein, the term xe2x80x9ccloned polynucleotidexe2x80x9d, refers to a polynucleotide or DNA sequence cloned in accordance with standard cloning procedures currently used in genetic engineering to relocate a segment of DNA, which may in particular be cDNA, i.e. enzymatically derived from RNA, from its natural location to a different site where it will be reproduced.
Cloning may be accomplished by excision and isolation of the desired DNA segment, insertion of the piece of DNA into the vector molecule and incorporation of the recombinant vector into a cell where multiple copies or clones of the DNA segment will be replicated, by reverse transcription of mRNA (reverse transcriptase technology), and by use of sequence-specific oligonucleotides and DNA polymerase in a polymerase chain reaction (PCR technology).
The cloned polynucleotide of the invention may alternatively be termed xe2x80x9cDNA constructxe2x80x9d or xe2x80x9cisolated DNA sequencexe2x80x9d, and may in particular be a complementary DNA (cDNA).
It is well established that potassium channels may be formed as heteromeric channels, composed of different subunits. Also it has been established that the potassium channel of the invention may form heteromers with other KCNQ""s, in particular KCNQ3 and KCNQ4, when co-expressed with these subunits. In addition, potassium channels can associate with non-homologous subunits (xcex2-subunits), e.g. the KCNE1 (also known as mink or lsK), the KCNE2 (also known as the mink-related peptide (MiRP1), the KCNE3 (also known as MiRP2), the KCNE4 (also known as MiRP3), and/or the KCNE5 (also known as KCNE1L) subunit, that co-assemble and functionally modulate these channels or lead to a specific localisation within the cell.
Therefore, in a preferred embodiment, the polynucleotide of the invention is cloned and either expressed by itself or co-expressed with polynucleotides encoding other subunits, in particular a polynucleotide encoding a KCNQ3 channel subunit or a polynucleotide encoding a KCNQ4 channel subunit.
In another aspect of the invention, isolated and purified KCNQ5 antisence oligonucleotides can be made and a method utilised for diminishing the level of expression of KCNQ5 by a cell comprising administering one or more KCNQ5 antisense oligonucleotides. By KCNQ5 antisense oligonucleotides reference is made to oligonucleotides that have a nucleotide sequence that interacts through base pairing with a specific complementary nucleic acid sequence involved in the expression of KCNQ5 such that the expression of KCNQ5 is reduced. Preferably, the nucleic acid sequence involved in the expression of KCNQ5 is a genomic DNA molecule or mRNA molecule that encodes KCNQ5. This genomic DNA molecule can comprise regulatory regions of the KCNQ5 gene, the pre- or pro-portions of the KCNQ5 gene, or the coding sequence for mature KCNQ5 protein.
The term xe2x80x9ccomplementary to a nucleotide sequencexe2x80x9d in the context of KCNQ5 antisense oligonucleotides and methods therefor means sufficiently complementary to such a sequence as to allow hybridization to that sequence in a cell, i.e. under physiological conditions. The KCNQ5 antisense oligonucleotides preferably comprise a sequence comprising of from about 8 to about 100 nucleotides, more preferably of from about 15 to about 30 nucleotides.
The KCNQ5 antisense oligonucleotides can also include derivatives which comprise a variety of modifications that confer resistance to nucleolytic degradation such as e.g. modified internucleoside linkages modified nucleic acid bases and/or sugars and the like. Examples of such derivatives include backbone modifications such as phosphotriester, phosphorothioate, methylphosphate, phosphoramidate, phosphorodithioate and formacetal as well as morpholino, peptide nucleic acid analogues and dithioate repeating units.
The usefulness of antisense molecules have been described by e.g. Toulme and Helene, Gene 1988 72 51-58; Inouye, Gene 1988 72 25-34; Uhlmann and Peyman, Chemical Reviews 1990 90 543-584; Robertson, Nature Biotechnology 1997 15 209; and Gibbons and Dzau, Science 1996 272 689-693, which publications are hereby incorporated by reference.
Biological Sources
The isolated polynucleotide of the invention may be obtained from any suitable human or animal source. In a preferred embodiment, which the polynucleotide of the invention is cloned from, or produced on the basis of a cDNA library, e.g. of the retina, skeletal muscle, or brain, in particular the cerebral cortex, occipital pole, frontal and temporal lobes, putamen and the hippocampus, and in the piriform cortex, the entorhinal cortex, the pontine medulla and the facial nucleus, and in the cerebellum. In a more preferred embodiment, which the polynucleotide of the invention is cloned from, or produced on the basis of a CDNA library of the thalamus. Commercial cDNA libraries are available from e.g. Stratagene and Clontech.
The KCNQ5 gene of the invention has been localised to the long arm of chromosome 6 (6q14).
The isolated polynucleotide of the invention may be obtained methods known in the art, e.g. those described in the working examples below.
Preferred Polynucleotides
In a preferred embodiment, polynucleotide of the invention has the polynucleotide sequence presented as SEQ ID NO: 1.
In another preferred embodiment the polynucleotide of the invention is a sequence giving rise to KCNQ5 channels subunits comprising one or more substitutions.
In another preferred embodiment the polynucleotide of the invention is a sequence giving rise to KCNQ5 channels subunits comprising one or more substitutions in the conserved regions, as defined in more details below.
It has been demonstrated that KCNQ channels often show alternative splicing and therefore may occur as isoforms originating from the same gene. Such isoforms as well as the different cDNA sequences from which they occurred are also contemplated within the scope of the present invention.
Finally the genes encoding KCNQ channel subunits in other species have been found to differ slightly from the human genes. However, genes of other species, e.g. mouse, rat, monkey, rabbit, etc., are also contemplated within the scope of the present invention.
In another aspect the invention relates to novel KCNQ5 proteins. More specifically, the invention relates to substantially pure functional polypeptides that have the electrophysiological and pharmacological properties of a KCNQ5 channel, or KCNQ5 channel subunits. The novel polypeptides of the invention may be obtained by the polynucleotides of the invention using standard recombinant DNA technology.
In a preferred embodiment, a polypeptide of the invention is the KCNQ5 potassium channel having the amino acid sequence presented as SEQ ID NO: 2, and biologically active fragments hereof.
Modifications of this primary amino acid sequence may result in proteins which have substantially equivalent activity as compared to the unmodified counterpart polypeptide, and thus may be considered functional analogous of the parent proteins. Such modifications may be deliberate, e.g. as by site-directed mutagenesis, or they may occur spontaneous, and include splice variants, isoforms, homologues from other species, and polymorphisms. Such functional analogous are also contemplated according to the invention.
Moreover, modifications of this primary amino acid sequence may result in proteins which do not retain the biological activity of the parent protein, including dominant negative forms, etc. A dominant negative protein may interfere with the wild-type protein by binding to, or otherwise sequestering regulating agents, such as upstream or downstream components, that normally interact functionally with the polypeptide. Such dominant negative forms are also contemplated according to the invention.
In the context of this invention, the term xe2x80x9cvariant polypeptidexe2x80x9d means a polypeptide (or protein) having an amino acid sequence that differs from the sequence presented as SEQ ID NO: 2 at one or more amino acid positions. Such variant polypeptides include the modified polypeptides described above, as well as conservative substitutions, splice variants, isoforms, homologues from other species, and polymorphisms.
As defined herein, the term xe2x80x9cconservative substitutionsxe2x80x9d denotes the replacement of an amino acid residue by another, biologically similar residue. Examples of conservative substitutions include the substitution of one hydrophobic residue such as isoleucine, valine, leucine or methionine for another, or the substitution of one polar residue for another, such as the substitution of arginine for lysine, glutamic for aspartic acid, or glutamine for asparagine, and the like. The term conservative substitution also include the use of a substituted amino acid residue in place of an un-substituted parent amino acid residue provided that antibodies raised to the substituted polypeptide also immune-react with the un-substituted polypeptide.
KCNQ1 Numbering System
In the context of this invention, amino acid residues (as well as nucleic acid bases) are specified using the established one-letter symbol.
By aligning the amino acid sequences of a polypeptide of the present invention to those of the known polypeptides, a specific amino acid numbering system may be employed, by which system it is possible to unambiguously allot an amino acid position number to any amino acid residue in any KNCQ channel protein, which amino acid sequence is known.
Such an alignment is presented in Table 1, below. Using the ClustalX computer alignment program [Thompson J D, Gibson T J, Piewniak F, Jeanmougin F, and Higgins D G: The ClustalX windows interface: flexible strategies for multiple sequence alignment aided by quality analysis tools; Nucleic Acids Res. 1997 25 (24) 4876-82], and the default parameters suggested herein, the amino acid sequence of a polypeptide of the present invention (hKCNQ5) and the amino acid sequences of the known polypeptides hKCNQ2-4 are aligned with, and relative to, the amino acid sequences of the known polypeptide hKCNQ1 (also known as KvLQT1). In the context of this invention this numbering system is designated the KCNQ1 Numbering System.
In describing the various enzyme variants produced or contemplated according to the invention, the following nomenclatures have been adapted for ease of reference:
Original Amino Acid/Position/Substituted Amino Acid
According to this nomenclature the substitution of serine for glycine at position 329 of Table 1 is designated as xe2x80x9cG329Sxe2x80x9d.
Preferred variants are the splice variants at positions 432-476 (KCNQ1 Numbering) holding the following amino acid residues:
Another preferred variants is G329S (KCNQ1 numbering), or KCNQ5/G278S (xe2x80x9cKCNQ5 numberingxe2x80x9d).
Ion channels are excellent targets for drugs. The polynucleotide of the invention encodes a potassium channel, which has been termed KNCQ5.
KCNQ5, or heteromeric channels containing the KCNQ5 subunit, may be a particularly interesting target for the treatment of diseases or adverse conditions of the CNS, including affective disorders, Alzheimer""s disease, anxiety, ataxia, CNS damage caused by trauma, stroke or neurodegenerative illness, cognitive deficits, compulsive behaviour, dementia, depression, Huntington""s disease, learning deficiencies, mania, memory impairment, memory disorders, memory dysfunction, motion disorders, motor disorders, motor neuron doseases, myokymia, neurodegenerative diseases, Parkinson""s disease and Parkinson-like motor disorders, phobias, Pick""s disease, psychosis, schizophrenia, seizures, incl. epileptic seizures, spinal cord damage, stroke, tremor, seizures, convulsions and epilepsy.
The novel polynucleotides of the invention may in itself be used as a therapeutic or diagnostic agent. For gene therapy, the person skilled in the art may use sence or antisense nucleic acid molecules as therapeutic agents for KCNQ-related indications.
Heteromers Formed by KCNQ Subunits
The KCNQ channels described so far function physiologically as heteromers. KCNQ1 associates with KCNE1 (also known as minK or lsK); KCNQ2 and KCNQ3 form heteromeric channels that underlie the M-current, an important determinant of neuronal excitability that is regulated by several neurotransmitters, and KCNQ4 is supposed to combine with KCNQ3 to mediate the IM-like current in the outer hair cells.
Like other KCNQ channel subunits, KCNQ5 may interact with other subunits, e.g. KCNE1 or other KCNQ channel subunits, and in particular with KCNQ3, and with KCNQ4. Currents from homomeric KCNQ3 are very small and often cannot be distinguished from Xenopus oocyte background currents. Co-expression of KCNQ3 with KCNQ5 markedly increased current amplitudes. Co-expression of KCNQ4 with KCNQ5 markedly decreased current amplitudes.
The polypeptides of the invention can be used to produce antibodies which are immunoreactive or bind to epitopes of these polypeptides. Polyclonal antibodies which consist essentially of pooled monoclonal antibodies with different specificities, as well as distinct monoclonal antibody preparations may be provided. Polyclonal antibodies which are made up of pooled monoclonal antibodies with different specificities, as well as distinct monoclonal antibody preparations may be provided.
The preparation of polyclonal and monoclonal antibodies is well known in the art. Polyclonal antibodies may in particular be obtained as described by e.g. Green et al.: xe2x80x9cProduction of Polyclonal Antiseraxe2x80x9d in Immunochemical Protocols (Manson, Ed.); Humana Press, 1992, Pages 1-5; Coligan et al.: xe2x80x9cProduction of Polyclonal Antisera in rabbits, rats, Mice and Hamstersxe2x80x9d in Current Protocols in Immunology, 1992, Section 2.4.1; and Ed Harlow and David Lane (Eds.) in xe2x80x9cAntibodies; A laboratory manualxe2x80x9d, Cold Spring Harbor Lab. Press 1988; which protocols are hereby incorporated by reference.
Monoclonal antibodies may in particular be obtained as described by e.g. Kohler and Milstein, Nature 1975 256 495; Coligan et al. in Current Protocols in Immunology, 1992, Sections 2.5.1-2.6.7; Harlow et al. in Antibodies: A Laboratory Manual; Cold Spring Harbor Pub., 1988, Page 726; which protocols are hereby incorporated by reference.
Briefly, monoclonal antibodies may be obtained by injecting e.g. mice with a composition comprising an antigen, verifying the presence of antibody production by removing a serum sample, removing the spleen to obtain B lymphocytes, fusing the B lymphocytes with myeloma cells to produce hybridomas, cloning the hybridomas, selecting positive clones that produce the antibodies to the antigen, and isolating the antibodies from the hybridoma cultures.
Monoclonal antibodies can be isolated and purified from hybridoma cultures by a variety of well-established techniques, including affinity chromatography with protein A Sepharose, size-exclusion chromatography, and ion-exchange chromatography, see. e.g. Coligan et al. in Current Protocols in Immunology, 1992, Sections 2.7.1-2.7.12, and Sections 2.9.1-2.9.3; and Bames et al.: xe2x80x9cPurification of Immunoglobulin G (IgG)xe2x80x9d in Methods in Molecular Biology; Humana Press, 1992, Vol. 10, Pages 79-104.
The polyclonal or monoclonal antibodies may optionally be further purified, e.g. by binding to and elution from a matrix to which the polypeptide, to which the antibodies were raised, is bound.
Antibodies which bind to the polypeptide of the invention can be prepared using an intact polypeptide or fragments containing small peptides of interest as the immunising antigen. The polypeptide used to immunise an animal may be obtained by recombinant DNA techniques or by chemical synthesis, and may optionally be conjugated to a carrier protein. Commonly used carrier proteins which are chemically coupled to the peptide include keyhole limpet hemocyanin (KLH), thyroglobulin, bovine serum albumin (BSA), and tetanus toxoid. The coupled peptide may then be used to immunise the animal, which may in particular be a mouse, a rat, a hamster or a rabbit.
In a third aspect the invention provides a cell genetically manipulated by the incorporation of the heterologous polynucleotide of the invention. The cell of the invention may in particular be genetically manipulated to transiently or stably express, over-express or co-express a KCNQ5 channel subunit as defined above. Methods of transient and stable transfer are known in the art.
The polynucleotide of the invention may be inserted into an expression vector, e.g. a plasmid, virus or other expression vehicle, and operatively linked to expression control sequences by ligation in a way that expression of the coding sequence is achieved under conditions compatible with the expression control sequences. Suitable expression control sequences include promoters, enhancers, transcription terminators, start codons, splicing signals for introns, and stop codons, all maintained in the correct reading frame of the polynucleotide of the invention so as to permit proper translation of mRNA. Expression control sequences may also include additional components such as leader sequences and fusion partner sequences.
The promoter may in particular be a constitutive or an inducible promoter. When cloning in bacterial systems, inducible promoters such as pL of bacteriophage xcex3, plac, ptrp, ptac (ptrp-lac hybrid promoter), may be used. When cloning in mammalian systems, promoters derived from the genome of mammalian cells, e.g. the TK promoter or the metallothionein promoter, or from mammalian viruses, e.g. the retrovirus long terminal repeat, the adenovirus late promoter or the vaccinia virus 7.5K promoter, may be used. Promoters obtained by recombinant DNA or synthetic techniques may also be used to provide for transcription of the polynucleotide of the invention.
Suitable expression vectors typically comprise an origin of expression, a promoter as well as specific genes which allow for phenotypic selection of the transformed cells, and include vectors like the T7-based expression vector for expression in bacteria [Rosenberg et al; Gene 1987 56 125], the pMSXND expression vector for expression in mammalian cells [Lee and Nathans, J. Biol. Chem. 1988 263 3521], baculovirus derived vectors for expression in insect cells, and the oocyte expression vector PTLN [Lorenz C, Pusch M and Jentsch T J: Heteromultimeric CLC chloride channels with novel properties; Proc. Natl. Acad. Sci. USA 1996 93 13362-13366].
In a preferred embodiment, the cell of the invention is an eukaryotic cell, in particular a mammalian cell, an oocyte, or a yeast cell. In a more preferred embodiment, the cell of the invention is a human embryonic kidney (HEK) cell, a HEK 293 cell, a BHK21 cell, a Chinese hamster ovary (CHO) cell, a Xenopus laevis oocyte (XLO) cell, a COS cell, or any other cell line able to express KCNQ potassium channels.
When the cell of the invention is an eukaryotic cell, incorporation of the heterologous polynucleotide of the invention may be in particular be carried out by infection (employing a virus vector), by transfection (employing a plasmid vector), or by calcium phosphate precipitation, microinjection, electroporation, lipofection, or other physical-chemical methods known in the art.
In a further preferred embodiment, the cell of the invention is genetically manipulated to co-express KCNQ5 and KCNQ1 channel subunits; KCNQ5 and KCNQ2 channel subunits; KCNQ5 and KCNQ3 channel subunits; KCNQ5 and KCNQ4 channel subunits; KCNQ5 and KCNQ1 and KCNQ2 channel subunits; KCNQ5 and KCNQ1 and KCNQ3 channel subunits; KCNQ5 and KCNQ2 and KCNQ3 channel subunits; KCNQ5 and KCNQ1 and KCNQ4 channel subunits; KCNQ5 and KCNQ2 and KCNQ4 channel subunits; KCNQ5 and KCNQ3 and KCNQ4 channel subunits; KCNQ5 and KCNQ1 and KCNQ2 and KCNQ3 channel subunits; KCNQ5 and KCNQ1 and KCNQ2 and KCNQ4 channel subunits; KCNQ5 and KCNQ1 and KCNQ3 and KCNQ4 channel subunits, or KCNQ5 and KCNQ2 and KCNQ3 and KCNQ4 channel subunits.
In another preferred embodiment, membrane preparations are provided. The membrane preparations of the invention may typically be used for screening purposes, and may be obtained by standard techniques.
In a preferred embodiment, frozen intact cells of the invention are homogenised while in cold water suspension and a membrane pellet is collected after centrifugation. The pellet may then be washed in cold water and dialysed to remove endogenous ligands that could compete for binding in the assays. The dialysed membranes may be used as such, or after storage in lyophilised form.
In another aspect the invention relates to chemical compounds capable of binding to, and showing activity at potassium channels containing one or more KCNQ5 subunits. In the context of this invention such compounds are termed KCNQ5 active compounds.
The KCNQ5 active compounds of the invention have therapeutic potential, and may be used for the manufacture of pharmaceutical compositions.
The KCNQ5 active compounds of the invention may in particular be used in diagnosis, treatment, prevention or alleviation of diseases related to diseases or adverse conditions of the CNS, including affective disorders, Alzheimer""s disease, anxiety, ataxia, CNS damage caused by trauma, stroke or neurodegenerative illness, cognitive deficits, compulsive behaviour, dementia, depression, Huntington""s disease, mania, memory impairment, memory disorders, memory dysfunction, motion disorders, motor disorders, neurodegenerative diseases, Parkinson""s disease and Parkinson-like motor disorders, phobias, Pick""s disease, psychosis, schizophrenia, spinal cord damage, stroke, tremor, seizures, convulsions and epilepsy.
Currently two compounds have been identified. As a preferred embodiment the invention therefore provides 1,3-dihydro-1-phenyl-3,3-bis-(4-pyridylmethyl)-2H-indol-2-one (Linopirdine) and 10,10-bis-(4-pyridinyl-methyl)-9-(10H)-antracenone (XE991) for use in the manufacture of a pharmaceutical composition for the diagnosis, treatment, prevention or alleviation of the above diseases.
In a further aspect the invention provides methods for screening for KCNQ5 active compounds, i.e. chemical compounds capable of binding to, and showing activity at potassium channels containing one or more KCNQ5 subunits. The activity determined may be inhibitory activity, stimulating activity, or other modulatory activity. In particular the KCNQ5 active compound may induce a second messenger response, which cause a change of the molecular characteristics of the cell, e.g. the ion flux, enzyme activation, changes in the level of intracellular Ca2+or H+, changes cyclic nucleotides such as cAMP, cADP, cGMP, and cGDP, etc.
Therefore, in another aspect, the invention provides a method for identifying functional ligands for a human potassium channel, comprising a KCNQ5 subunit, which method comprises transfecting cells with one or more polypeptides of the invention, encoding a KCNQ5 channel subunit, and detecting the effect on the signal transduction pathway caused in these cells by binding of the ligands to the receptor by a reporter system.
Such chemical compounds can be identified by one of, or both methods described below.
Binding Studies
Binding studies are usually carried out by subjecting the target to binding with a labelled, selective agonist (binding agent), to form a labelled complex, followed by determination of the degree of displacement caused by the test compound upon addition to the complex.
In a specific aspect the invention provides a method of screening a chemical compound for capability of binding to a potassium channel comprising at least one KCNQ5 channel subunit, which method comprises the steps of (i) subjecting a KCNQ5 channel subunit containing cell to the action of a KCNQ5 binding agent to form a complex with the KCNQ5 channel subunit containing cell; (ii) subjecting the complex of step (i) to the action of the chemical compound to be tested; and (iii) detecting the displacement of the KCNQ5 binding agent from the complex with the KCNQ5 channel subunit containing cell.
The KCNQ5 channel subunit containing cell preferably is a cell of the invention as described above.
The KCNQ5 binding agent preferably is a radioactively labelled 1,3-dihydro-1-phenyl-3,3-bis-(4-pyridylmethyl)-2H-indol-2-one (Linopirdine); or 10,10-bis-(4-pyridinyl-methyl)-9-(1OH)-antracenone (XE991).
In a even more preferred embodiment, the binding agent is labelled with 3H, and the displacement of the KCNQ5 binding agent from the complex with the KCNQ5 channel subunit containing cell is detected by measuring the amount of radioactivity by conventional liquid scintillation counting.
Activity Studies
The KCNQ5 channel agonists may affect the potassium channel in various ways. The agonist may in particular show inhibitory activity, stimulating activity, or other modulatory activity.
In a specific aspect the invention provides a method for determining the activity at potassium channels containing one or more KCNQ5 subunits. According to this method a KCNQ5 channel subunit containing cell is subjecting to the action of the chemical compound to be tested, and the activity is detected by way of monitoring the membrane potential, the current, the potassium flux, or the secondary calcium influx of the KCNQ5 channel subunit containing cell, preferably a genetically manipulated as described above.
The membrane potential and the current may be monitored by electrophysiologic methods, including patch clamp techniques, such as current clamp technology and two-electrode voltage clamp technology, or by spectroscopic methods, such as fluorescence methods.
In a preferred embodiment, monitoring of the membrane potential of the KCNQ5 channel subunit containing cell is performed by patch clamp techniques.
In another preferred embodiment, monitoring of the membrane potential of the KCNQ5 channel subunit containing cell is performed by spectroscopic methods, e.g. using fluorescence methods. In a more specific embodiment, the KCNQ5 channel subunit containing cell is mixed with a membrane potential indicating agent, that allow for a determination of changes in the membrane potential of the cell, caused by the addition of the test compound. The membrane potential indicating agent may in particular be a fluorescent indicator, preferably DIBAC4(3), DiOC5(3), and DiOC2(3).
In yet a preferred embodiment, monitoring of the membrane potential of the KCNQ5 channel subunit containing cell is performed by spectroscopic methods, e.g. using a FLIPR assay (Fluorescence Image Plate Reader; available from Molecular Devices).
In a further aspect the invention relates to the use of a polynucleotide sequence of the invention for the screening of genetic materials. By this method, individuals bearing a gene identical or homologous to a polynucleotide of the invention may be identified.
In the screening method of the invention, a polynucleotide of the invention, or any fragment or sub-sequence hereof, is employed. For the identification of individuals bearing mutated genes preferably the mutated forms of the polynucleotide represented by SEQ ID NO: 1 are employed.
In the screening method of the invention only short sequences needs to be employed depending on the actual method used. For SSCA, several hundreds of base pairs may be needed, for oligonucleotide or PCR hybridisation only of from about 10 to about 50 basepairs may be needed.
The screening may be accomplished by conventional methods, including hybridisation, SSCA analysis, and microarray technology (DNA chip technology). The hybridisation protocol described above represents a suitable protocol for use in a screening method of the invention.
Transgenic animal models provide the means, in vivo, to screen for therapeutic compounds. Since KCNQ5 is expressed also in brain, they may be helpful in screening for drugs effective in CNS disorders, e.g. epilepsy.
By transgene is meant any piece of polynucleotide which is inserted by artifice into a cell, and thus becomes part of the genome of the organism that develops from that cell. Such a transgene may include a gene which is partly or entirely heterologous (i.e. foreign) to the transgenic organism, or it may represent a gene homologous to an endogenous gene of the organism.
By a transgenic animal is meant any organism holding a cell which includes a polynucleotide sequence which is inserted into that cell by artifice, and which cell becomes part of the transgenic organism which develops from that cell. Such a transgene may be partly or entirely heterologous to the transgenic animal. Although transgenic mice represent a preferred embodiment of the invention, other transgenic mammals including, but not limited to transgenic rodents (e.g. hamsters, guinea pigs, rabbits and rats), and transgenic pigs, cattle, sheep and goats may be created by standard techniques and are included in the invention.
Preferably, the transgene is inserted by artifice into the nuclear genome.
Knock-out and Knock-in Animals
The transgenic knock-out animal models may be developed by homologous recombination of embryonic stem cells with constructs containing genomic sequence from the KCNQ5 gene, that lead to a loss of function of the gene after insertion into the endogenous gene.
By knock-out mutation is meant an alteration in the polynucleotide sequence that reduces the biological activity of the polypeptide normally encoded therefrom. In order to create a true knock-out model, the biological activity of the expressed polypeptide should be reduced by at least 80% relative to the un-mutated gene. The mutation may in particular be a substitution, an insertion, a deletion, a frameshift mutation, or a mis-sense mutation. Preferably the mutation is a substitution, an insertion or a deletion.
To further assess the role of KCNQ5 at an organism level, the generation of an animal, preferably a mouse, lacking the intact KCNQ5 gene, or bearing a mutated KCNQ5 gene, is desired.
A replacement-type targeting vector, which may be used to create a knock-out model, may be constructed using an isogenic genomic clone, e.g. from a mouse strain such as 129/Sv (Stratagene Inc., La Jolla, Calif.). The targeting vector may be introduced into a suitably-derived line of embryonic stem (ES) cells by electroporation to generate ES cell lines that carry a profoundly truncated form of the KCNQ5 gene. The targeted cell lines may then be injected into a mouse blastula stage embryo to generate chimeric founder mice. Heterozygous offspring may be interbred to homozygosity.
Animal models for over-expression may be generated by integrating one or more polynucleotide sequence of the invention into the genome according to standard techniques.
The procedures disclosed herein involving the molecular manipulation of nucleic acids are known to those skilled in the art, and are described by e.g. Fredrick M A et al. [Fredrick M A et al.: Short Protocols in Molecular Biology; John Wiley and Sons, 1995] and Sambrook et al. [Sambrook et al.: Molecular Cloning: A Laboratory Manual; 2. Ed., Cold Spring Harbor Lab.; Cold Spring Harbor, N.Y. 1989], and in Alexandra L J (Ed.): Gene Targeting: A practical approach; Oxford University Press (Oxford, New York, Tokyo), 1993.